Without limiting the scope of the invention, its background is described in connection with power FET devices, as an example.
In the field of highly integrated electronics, previous power distribution practices and power supply technologies were not adequate to supply well regulated power to using circuitry. The concept of centralized power with decoupled loads simply has not worked well. The power distribution problem is moving from standard design techniques to real point-of-use regulators in the form of high-efficiency switching power supplies. Such power supplies are typically and more efficient than previous power supplies.
GaAs VFETs are attractive for high-efficiency switching power supplies. Several studies have concluded that the intrinsic devices have a factor of 5 to 8 lower on-resistance per unit area, as compared to state-of-the-art DMOS or UMOS power devices fabricated by the most advanced processes available. In addition, GaAs VFETs have excellent switching speed. Therefore, with such a device, the efficiency of switching power supplies can be significantly improved.
Previously filed applications, U.S. Pat. No. 5,231,037 filed Apr. 30, 1992 and U.S. Pat. No. 5,342,795 filed Nov. 15, 1993, both by Yuan et al., introduced VFETs using carbon as a low diffusion, high concentration p-type gate dopant. These VFETs increased the potential uses of GaAs Power VFETs. Specifically, buried carbon gate electrodes may be used to design VFETs with channel openings less than 1.0 .mu.m. Meanwhile, the high doping concentration (.apprxeq.10.sup.20 cm.sup.-3) can make the gate sheet resistance acceptable for converter type (&gt;1 MHz switching) rectifier applications. In comparison to the most advanced UMOS power transistors previously reported, the GaAs VFET using the carbon gate electrodes is superior in the four categories that are important to the design of a low-loss, high-efficiency switching power supply: on-resistance, junction capacitance, gate resistance, and gate driving voltage. Furthermore, the new GaAs VFETs can be switched in less than 2 ns, while the UMOS power devices generally require at least 50 ns to switch because of much higher gate resistance. The GaAs VFETs fabricated using the carbon doped gate can also be used for other applications such as high-power microwave amplifiers and high-gain photodetectors.